Digital broadcast system and data processing method

ABSTRACT

A digital broadcast system and a data processing method are disclosed. A data processing method of a digital broadcast transmission system includes delaying a reference time of a program clock reference (PCR) based on a size of mobile service data, when processing a broadcasting signal including main service data and the mobile service data, verifying a transport stream system target decoder (T-STD) model based on the PCR of the delayed reference time, and storing a packet of the main service data in an auxiliary buffer, when overflow of a buffer in the T-STD model is estimated as the verification result of the T-STD model.

This application claims the benefit of 61/029,550, filed on Feb. 18,2008, which is hereby incorporated by reference as if fully set forthherein. Also, this application claims the benefit of Korean ApplicationNo. 10-2009-0012635, filed on Feb. 16, 2009, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a digital broadcast system, and moreparticularly, to a digital broadcast transmission system, a digitalbroadcast receiver, and a data processing method of the digitalbroadcast transmission system and the digital broadcast receiver.

2. Discussion of the Related Art

A digital broadcast system may include a digital broadcast transmitterand a digital broadcast receiver. The digital broadcast transmitterdigitally processes data of a broadcasting program etc. and transmitsthe processed data to the digital broadcast receiver. Such a digitalbroadcast system is replacing an analog broadcast system, due to variousadvantages such as the efficiency of data transmission.

Recently, research into the digital broadcast receiver, which is capableof receiving broadcasting signals while moving, has been conducted. Adigital broadcast transmission system can transmit both broadcastingsignals for a fixed digital broadcast receiving system and broadcastingsignals for a mobile digital broadcast receiving system.

However, according to the prior art, if the broadcasting signals for themobile digital broadcast receiving system are simply added to thebroadcasting signals for the fixed digital broadcast receiving system,an unexpected overflow or underflow problem in a buffer occursfrequently.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a digital broadcastsystem and a data processing method that substantially obviate one ormore problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a digital broadcastsystem and a data processing method which do not generate an overflow orunderflow problem even when both broadcasting signals for a fixeddigital broadcast receiving system and broadcasting signals for a mobiledigital broadcast receiving system are processed.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, adata processing method of a digital broadcast transmission systemincludes delaying a reference time of a program clock reference (PCR)based on a size of mobile service data, when processing a broadcastingsignal including main service data and the mobile service data,verifying a transport stream system target decoder (T-STD) model basedon the PCR of the delayed reference time, and storing a packet of themain service data in an auxiliary buffer, when overflow of a buffer inthe T-STD model is estimated as the verification result of the T-STDmodel.

In another aspect of the present invention, a data processing method ofa digital broadcast receiver includes receiving a broadcasting signalincluding a main service data packet, a mobile service data packet, anda program clock reference (PCR), reference time of which is delayed,wherein the broadcasting signal includes a null data packet instead ofthe main service data packet, according to a result of a verificationprocess of the T-STD model of a digital broadcast transmission system,demultiplexing the received broadcasting signal, and decoding the mainservice data packet, which is demultiplexed, according to the PCR.

In a further aspect of the present invention, a digital broadcasttransmission system includes a delay for delaying a reference time of aprogram clock reference (PCR) based on a size of mobile service data,when processing a broadcasting signal including main service data andthe mobile service data, a verifier for verifying a transport streamsystem target decoder (T-STD) model based on the PCR of the delayedreference time, and an auxiliary buffer for storing a packet of the mainservice data according to a verification result of the T-STD model.

In another aspect of the present invention, a digital broadcast receiverincludes a receiver for receiving a broadcasting signal including a mainservice data packet, a mobile service data packet, and a program clockreference (PCR), reference time of which is delayed, wherein thebroadcasting signal includes a null data packet instead of the mainservice data packet, according to a result of a verification process ofthe T-STD model of a digital broadcast transmission system, ademultiplexer for demultiplexing the received broadcasting signal, and adecoder for decoding the main service data packet, which isdemultiplexed, according to the PCR.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram illustrating the construction of a T-STD whichis one type of digital broadcast transmission system;

FIG. 2 is a block diagram illustrating the construction of a digitalbroadcast transmission system according to an exemplary embodiment ofthe present invention;

FIG. 3 is a diagram illustrating fullness of data stored in a transportbuffer of the T-STD of FIG. 1, when only main service data is processedwithout mobile service data;

FIG. 4 is a diagram illustrating fullness of data stored in a transportbuffer of the T-STD of FIG. 1, when both mobile service data and mainservice data are processed;

FIG. 5 is a diagram illustrating fullness of data stored in a mainbuffer of the T-STD of FIG. 1 before PCR adjustment, when both mobileservice data and main service data are processed;

FIG. 6 is a diagram illustrating fullness of data stored in a transportbuffer of the T-STD of FIG. 1 after PCR adjustment, when both mobileservice data and main service data is processed;

FIG. 7 is a flow chart illustrating a data processing method of adigital broadcast transmission system according to an exemplaryembodiment of the present invention; and

FIG. 8 is a block diagram illustrating a digital broadcast receiveraccording to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The exemplary embodiments of the invention may be modified invarious forms and the invention should not be limited to the specificembodiments described herein.

Although the terms used in the present invention are selected fromgenerally known and used terms while considering functions of thepresent invention, they may vary according to intention or customs ofthose skilled in the art or to emergence of new technology. Some of theterms mentioned in the description of the present invention may havebeen selected by the applicant at his or her discretion, and in suchcases the detailed meanings thereof will be described in relevant partsof the description herein. Thus, the terms used in this specificationshould be interpreted based on the substantial meanings of the terms andthe whole content of this specification rather than their simple namesor meanings.

Among the terms used in the description of the present invention, mainservice data corresponds to data that can be received by a fixedreceiving system and may include audio/video (A/V) data. Morespecifically, the main service data may include high definition (HD) orstandard definition (SD) A/V data and may also include diverse datatypes required for data broadcasting. Moreover, known data refers todata that is pre-known by an agreement between a receiving side and atransmitting side

Among the terms used in the description of the present invention, MHindicates respective first letters of the words “mobile” and “handheld”and is an opposite concept to a fixed type. MH service data may includeat least one of mobile service data and handheld service data, and willbe referred to as mobile service data for convenience of description.Herein, the mobile service data may include not only the MH service databut also any type of service data indicating mobile or portablecharacteristics. Therefore, the mobile service data according to thepresent invention is not limited only to the MH service data.

The above-described mobile service data may correspond to data havinginformation, such as program execution files, stock information, etc.,and may also correspond to A/V data. Particularly, the mobile servicedata may correspond to A/V data having lower resolution and lower datarate as compared to the main service data, as the service data forportable or mobile terminals (or a broadcast receiver). For example, ifan A/V codec that is used for a conventional main service is an MPEG-2codec, an MPEG-4 advanced video coding (AVC) or scalable video coding(SVC) having better image compression efficiency may be used as the A/Vcodec for the mobile service. Furthermore, any type of data may betransmitted as the mobile service data. For example, transport protocolexpert group (TPEG) data for broadcasting real-time transportationinformation may be transmitted as the mobile service data.

A data service using the mobile service data may include weatherforecast services, traffic information services, stock informationservices, viewer participation quiz programs, real-time polls,interactive education broadcast programs, gaming services, servicesproviding information on synopsis, character, background music, andfilming sites of soap operas, services providing information on pastmatch scores and player profiles, and sports achievements, and servicesproviding information programs classified by service, medium, time, andtheme for product information and product order. Herein, the presentinvention is not limited only to the services mentioned above.

A transmitting system of the present invention provides backwardcompatibility in the main service data so as to be received by aconventional receiving system. The main service data and the mobileservice data can be multiplexed on the same physical channel and then betransmitted.

FIG. 1 is a block diagram illustrating the construction of a transportstream system target decoder (I-STD) which is one type of digitalbroadcast transmission system. The T-STD may correspond to a movingpicture experts group 2 (MPEG2) T-STD. The T-STD performs models of adigital broadcast receiver and adjusts an encoder of the digitalbroadcast receiver using the modeling result. In FIG. 1, t(i) denotes aninput time of an i-th byte of a transport stream (TS), and a bit ratereceived at that time is about 19.39 Mbps for example.

Traveling paths of input TS packets are determined according to packetidentifiers (PIDs). Video packets pass through the uppermost path (e.g.,TB1 in FIG. 1), audio packets pass through a middle path (e.g., TBn inFIG. 1), and system control packets pass through the lowermost path(e.g., TBsys in FIG. 1).

In the specification of the present invention, a description will begiven centering on the audio packets but the present invention may beapplied to the video packets or the system control packets. Accordingly,the scope of the present invention should not be limited to the audiopackets of the embodiment, but defined by the accompanying claims andequivalents thereof.

In FIG. 1, a TBn 110 denotes a transport buffer, a Bn 120 denotes a mainbuffer, and a Dn 130 denotes a decoder.

The TBn 110 may have a size of 512 bytes. Data input to the TBn 110 istransmitted to the Bn 120 at a rate of RXn. The traveling rate to the Bn120 is 2 Mbps when the TBn 110 includes data and is 0 Mbps when the TBn110 does not include data. Overflow should not occur in the TBn 110.However, when both mobile service data and main service data areprocessed, an overflow problem in the TBn 110 is considered. A methodfor solving this problem will be described in detail with reference toother drawings.

The size of the Bn 120 may be 3,584 bytes or 2,592 bytes. A bit stream,that is input at a rate of RXn, is transmitted to the Dn 130 at a timetdn(j). In this case, tdn(j) is determined by a decoding time stamp(DTS) transmitted through the bit stream. A system time clock (STC) isrecovered using a program clock reference (PCR). At a time point whenthe recovered STC coincides with a DTS, data in the Bn 120 istransmitted to the Dn 130. Overflow and underfloor should not occur inthe Bn 120. However, when both the mobile service data and the mainservice data are processed, especially an overflow problem in the Bn 120arises. A method for solving this problem will be described in detailwith reference to other drawings.

FIG. 2 is a block diagram illustrating the construction of a digitalbroadcast transmission system according to an exemplary embodiment ofthe present invention. As illustrated in FIG. 2, a digital broadcasttransmission system 200 includes an MH frame controller 201, a packettiming/PCR adjustment unit 202, a packet multiplexer (MUX) 210, an MHframe encoder 205, a block processor 206, a signaling encoder 207, agroup formatter 208, a packet formatter 209, a modified data randomizer212, a systematic/non-systematic RS encoder 213, a data interleaver 214,a parity replacer 215, a non-systematic RS encoder 217, a modifiedtrellis encoder 216, a synchronization (Sync) MUX 218, a pilot inserter219, a modulator 220, a radio frequency (RF) up-converter 221, and anauxiliary buffer 203.

A module including the MH frame encoder 205, the block processor 206,the signaling encoder 207, the group formatter 208, and the packetformatter 209 may be refereed to as a pre-processor 204.

A module including the modified data randomizer 212, thesystematic/non-systematic RS encoder 213, the data interleaver 214, theparity replacer 215, the non-systematic RS encoder 217, and the modifiedtrellis encoder 216 may be referred to as a post-processor 211.

The packet MUX 210 multiplexes a main service data packet with a mobileservice data packet that is output from the packet formatter 209 inunits of 188 bytes, according to a predefined multiplexing scheme andoutputs the multiplexed packet to the modified data randomizer 212. Themultiplexing scheme can be adjusted by various parameters of a systemdesign.

Meanwhile, the MH frame encoder 205 performs at least one of an errorcorrection encoding process and an error detection encoding process whenmobile service data is input thereto. Then robustness is provided to themobile service data and burst errors that may occur during changes in apropagation environment are scattered, so that the mobile service datacan cope with the propagation environment that is extremely poor andvaries rapidly. The MH frame encoder 205 may include a process formixing mobile service data of a constant size in units of a row.

The error correction encoding process applies RS encoding and the errordetection encoding process applies cyclic redundancy check (CRC)encoding, as an exemplary embodiment. When performing the RS encoding,parity data to be used for error correction is generated, and whenperforming the CRC encoding, CRC data to be used for error detection isgenerated.

The RS encoding may use a forward error correction (FEC) structure. FECrefer to a technique for correcting errors generated in a transmissionprocess. The CRC data generated by the CRC encoding may be used toindicate whether the mobile service data is damaged by errors whilebeing transmitted through a channel. The present invention may use errordetection encoding methods other than the CRC encoding or may raiseoverall error correction capabilities of a receiving side using theerror correction encoding method.

The mobile service data that is encoded by the MH frame encoder 205 isinput to the block processor 206. The block processor 206 encodes theinput mobile service data at a code rate of G/H (where G<H) and outputsthe encoded data to the group formatter 208. Here, the signaling encoder207 may encode signaling data, independent of the MH frame encoder 205,and may transmit the encoded signaling data to the group formatter 208.

Namely, the block processor 206 divides the mobile service data input inbyte units into data of bit units, encodes G-bit data into H-bit data,and converts the encoded data of bit units into data of byte units. Forexample, if 1-bit input data is encoded into 2-bit data, then G=1 andH=2, and if 1-bit input data is encoded into 4-bit data, then G=1 andH=4. For convenience of description, the former case will be referred toas encoding at a code rate of ½ (or ½-rate encoding) and the latter casewill be referred to as encoding at a code rate of ¼ (or ¼-rateencoding).

Using ¼-rate encoding accomplishes higher error correction capabilitiesthan using ½-rate encoding because of a higher code rate. For such areason, assuming that data encoded at a code rate of ¼ in the groupformatter 208, which is located near an end part of the system, isallocated to a region where reception performance may be degraded anddata encoded at a code rate of ½ is allocated to a region having betterperformance, an effect of reducing the difference in performance can beobtained.

The block processor 206 may receive from the signaling encoder 207additional information data, such as signaling containing systeminformation etc. The ½ encoding or ¼-rate encoding is performed upon theadditional information data in the same way as the mobile service dataprocessing process. Thereafter, the additional information data such assignaling is regarded as the mobile service data and then is processed.The signaling information is necessary to receive and process datacontained in a data group in a receiver and may include data groupinformation, multiplexing information, etc.

Meanwhile, the group formatter 208 inserts the mobile service datagenerated from the block processor 206 into corresponding regions withina data group formed according to a predefined rule, inserts variousplace holders or known data related to data deinterleaving intocorresponding regions within the data group, and performsdeinterleaving.

The data group may be divided into at least one hierarchical region. Thetype of the mobile service data being inserted into each region may varyaccording to the characteristics of each hierarchical region. Eachregion may be divided based upon, for example, the reception performancewithin the data group.

The reason why the data group is divided into a plurality of regions isto use the regions according to different purposes. More specifically,regions in which no interference or less interference from the mainservice data may be considered to have a robust reception performance ascompared to regions having higher interference levels. In a system thatinserts known data into the data group and transmits the data, when itis desired that consecutively long known data be periodically insertedinto the mobile service data, the known data having a predeterminedlength may be periodically inserted in a region having no interferencefrom the main service data. However, in a region having interferencefrom the main service data, it is difficult to periodically insert knowndata and to insert consecutively long known data into such a region.

Further, the group formatter 208 inserts into the data group additionalinformation data, such as signaling, indicating overall transmissioninformation, independent of the mobile service data.

In addition to the encoded mobile service data generated from the blockprocessor 206, the group formatter 208 also inserts an MPEG header placeholder, a non-systematic RS parity place holder, and a main service dataplace holder, which are related to data deinterleaving in a laterprocess. The main service data place holder is inserted because themobile service data and the main service data are alternately mixed witheach other in regions based upon data after the data deinterleavingprocess is performed. For example, based upon the data output after datadeinterleaving, the MPEG header place holder may be allocated at thevery beginning of each packet.

The group formatter 208 inserts known data generated in accordance witha predetermined method or inserts a known data place holder forinserting the known data in a later process. Moreover, a place holderfor initializing the modified trellis encoder 216 is also inserted in acorresponding region. For example, the initialization data place holdermay be inserted in the beginning of the known data sequence.

The size of the mobile service data that can be inserted into one datagroup may vary according to the sizes of the trellis initialization orknown data, MPEG header, and RS parity place holders.

The output of the group formatter 208 is transmitted to the packetformatter 209. The packet formatter 209 removes the main service dataplace holder and the RS parity place holder that have been allocated forthe deinterleaving process from the deinterleaved input data. Then, thepacket formatter 209 collects the remaining portion and inserts an MPEGheader in a 4-byte MPEG header place holder.

When the group formatter 208 inserts the known data place holder, thepacket formatter 209 may insert actual known data in the known dataplace holder, or may directly output the known data place holder withoutmodification in order to perform replacement insertion in a laterprocess.

Thereafter, the packet formatter 209 identifies data within thepacket-formatted data group as described above, as a mobile service datapacket (i.e., MPEG TS packet) of a 188-byte unit, which is then providedto the packet MUX 210.

Meanwhile, if input data is a main service data packet, the modifieddata randomizer 212 randomizes the input data in the same way as aconventional randomizer. Namely, the modified data randomizer 212discards a synchronization byte within the main service data packet andrandomizes the remaining 187 bytes using a pseudo random byte generatedtherein. Thereafter, the modified data randomizer 212 outputs therandomized data to the systematic/non-systematic RS encoder 213.

However, if the input data is a mobile service data packet, the modifieddata randomizer 212 deletes a synchronization byte from the 4-byte MPEGheader included in the mobile service data packet and performsrandomization only upon the other 3 bytes. The modified data randomizer212 does not perform randomizing upon the other mobile service dataexcept for the MPEG header and outputs the mobile service data to thesystematic/non-systematic RS encoder 213.

The systematic/non-systematic RS encoder 213 performs an RS encodingprocess upon the data being randomized by the modified data randomizer212 or upon the data bypassing the modified data randomizer 212, so asto add a 20-byte RS parity. The processed data is output to the datainterleaver 214. If the input data corresponds to the main service datapacket, the systematic/non-systematic RS encoder 213 performs the samesystematic RS encoding process as in a conventional advanced televisionsystems committee (ATSC) vestigial sideband (VSB) system, thereby addingthe 20-byte RS parity to the end of 187-byte data. If the input datacorresponds to the mobile service data packet, thesystematic/non-systematic RS encoder 213 performs a non-systematic RSencoding process. At this point, the 20-byte RS parity obtained from thenon-systematic RS encoding process is inserted in a predetermined paritybyte location within the mobile service data packet.

The data interleaver 214 corresponds to a convolutional interleaver of abyte unit.

The output of the data interleaver 214 is input to the parity replacer215 and to the non-systematic RS encoder 217.

Meanwhile, in order to decide the output data of the modified trellisencoder 216, which is located after the parity replacer 215, as theknown data predefined according to an agreement between a transmittingside and a receiving side, a process of initializing a memory within themodified trellis encoder 216 is primarily required. That is, the memoryof the modified trellis encoder 216 should be initialized before theinput known data sequence is trellis-encoded.

In this case, the beginning portion of the input known data sequencecorresponds to the initialization data place holder inserted in thegroup formatter 208, rather than the actual known data. Therefore, aprocess of generating initialization data immediately before the inputknown data sequence is trellis-encoded and replacing the initializationdata place holder of the corresponding memory with the generatedinitialization data is required.

A value of the trellis memory initialization data is decided andgenerated based upon a memory status of the modified trellis encoder216. Further, due to the newly replaced initialization data, a processof newly calculating the RS parity and replacing the RS parity, which isoutput from the data interleaver 214, with the newly calculated RSparity is required.

Therefore, the non-systematic RS encoder 217 receives the mobile servicedata packet including the initialization data place holder, which is tobe replaced with the actual initialization data, from the datainterleaver 214 and also receives the initialization data from themodified trellis encoder 216.

The non-systematic RS encoder 217 replaces the initialization data placeholder within the input mobile service data packet with theinitialization data and eliminates the RS parity data that are added tothe mobile service data packet. Thereafter, the non-systematic RSencoder 217 calculates a new RS parity and outputs the RS parity to theparity replacer 215. Accordingly, the parity replacer 215 selects theoutput of the data interleaver 214 as data within the mobile servicedata packet and selects the output of the non-systematic RS encoder 217as the RS parity. The selected data is then output to the modifiedtrellis encoder 216.

Meanwhile, if the main service data packet is input, or if the mobileservice data packet, which does not include any initialization dataplace holders that are to be replaced, is input, the parity replacer 215selects the data and RS parity that are output from the data interleaver214. Then, the parity replacer 215 directly outputs the selected data tothe modified trellis encoder 216 without any modification.

The modified trellis encoder 216 converts data of a byte unit into dataof a symbol unit and performs a 12-way interleaving process so as totrellis-encode the received data. Thereafter, the modified trellisencoder 216 outputs the processed data to the synchronization MUX 218.

The synchronization MUX 218 inserts a field synchronization signal and asegment synchronization signal to the data output from the modifiedtrellis encoder 216 and, then, outputs the processed data to the pilotinserter 219.

The pilot inserter 219 inserts a pilot to the data received from thesynchronization MUX 218 and the modulator 220 VSB-modulates the datareceived from the pilot inserter 219. The modulated data is transmittedto each broadcast receiving system or a digital broadcast receiverthough the RF up-converter 221.

To prevent an underfloor or overflow phenomenon of a buffer due to apacket, the exemplary embodiment of the present invention may include,as illustrated in FIG. 2, the packet timing/PCR adjustment unit 202, theauxiliary buffer 203, and the MH frame controller 201.

It is assumed that the size of an MH frame is about 968 milliseconds(ms), and the MH frame may be divided into 5 subframes. Each subframe isdivided into 16 slots, each of which contains 156 consecutive TSpackets. Among the 156 TS packets, 118 TS packets are allocated as an MHdata region. The MH data region may mean a region in which the MHservice data is allocated. If much MH data is present, MH data can beallocated to more slots. The MH data may correspond to the mobileservice data.

Meanwhile, if the mobile service data is transmitted by allocating theMH data region as described above, a main service data packet cannot betransmitted at that moment. Therefore, a transmission order of the mainservice data packet that has not been transmitted should be changed sothat the main service data packet can be transmitted in a region exceptfor the region where the mobile service data is transmitted. The packettiming/PCR adjustment unit 202 is designed to perform such a function.

The packet timing/PCR adjustment unit 202 serves to correct changed timeinformation as the time location of the main service data packetincluding a PCR is changed. To prevent buffer overflow, the packettiming/PCR adjustment unit 202 changes the location of an audio packet.Further, to prevent buffer underflow that occurs according to thelocation change of the audio packet, the packet timing/PCR adjustmentunit 202 delays the reference time of the PCR.

To check whether underflow occurs in the buffers shown in FIG. 1, thefollowing assumption is made.

If the audio packet is sampled at 32 kHz and is encoded at 384 kbps, oneframe becomes 48 ms and a data size corresponds to 13 TS packets.Assuming that a DTS is set such that the audio packet is transmitted asfast as possible and is decoded as soon as transmission is completed,the size of data contained in the TBn 110 is shown in FIG. 3.

In FIG. 3, the horizontal axis corresponds to an index of a TS packetand the vertical axis indicates the size of data contained in the TBn110. The period from when data is stacked in the TBn 110 to when the TBn110 is empty corresponds to the period when one audio frame is shiftedto Bn from TBn.

As shown in FIG. 3, if 9.91 ms elapses after the first audio TS packetis input, the TBn 110 is empty again. After this time point, the audiodecoder such as the Dn 130 can decode the audio frame. That is, if a DTSvalue of an audio packetized elementary stream (PES) packet headercontained in the first TS packet corresponds to an STC value after 9.91ms elapses, underflow does not occur. Specifically, if a decodingprocess is performed in a region ‘a’ shown in FIG. 3, underflow does notoccur.

A phenomenon appearing when a main service data encoded stream istransmitted together with mobile service data will now be described.FIG. 4 shows the case where the mobile service data, that is, MH data ismaximally transmitted. As described previously, the 118 TS packets areconsecutively transmitted in the MH data. A main service data packetshould be transmitted between intervals or slots in which the MH data istransmitted. Then the moment when TBn is empty becomes 34.05 ms, whichis further delayed by 24.14 ms as compared to when the MH data is nolonger present in FIG. 3.

Even though the MH data, etc. is transmitted, if a decoding process thatdoes not consider the mobile service data is performed at any time pointin the region ‘a’ shown in FIG. 3, especially at an early time point inthe region ‘a’, without considering the MH data or mobile service data,a probability of generating underflow is high. This is because a datapacket is shifted to the audio decoder from the audio buffer under thestate that the Bn 120 is not completely filled with data.

Meanwhile, regions ‘b’, ‘c’, ‘d’, ‘e’, ‘f’, ‘g’, and ‘h’ may correspondto time zones when the main service data packet is not input.

The present invention is designed such that a PCR is adjusted in orderto prevent such an underflow phenomenon. Namely, by comparing FIG. 3with FIG. 4, which are obtained experimentally, the reference time ofthe PCR is delayed by more than 24.14 ms that is a time difference(34.05 ms-9.91 ms=24.14 ms) in FIG. 3 and FIG. 4. It is possible tosufficiently fill the main buffers by delaying a time at which thedecoder operates. The time of 24.14 ms is a value obtainedexperimentally and the underflow phenomenon may be eliminated to somedegree even if a time of 24 to 25 ms is applied.

According to another exemplary embodiment, not only the underflowphenomenon of the buffers, for example, the TBn 110 and the Bn 120 butalso the overflow phenomenon thereof is substantially eliminated.

In the above description, the case where the audio packet is transmittedas fast as possible and is decoded as soon as transmission is completedhas an underflow problem. Meanwhile, when the audio packet is designedsuch that the audio packet is transmitted rapidly but as much data aspossible is stacked in the main buffer Bn 120, an overflow problemoccurs.

FIG. 5 shows a main buffer different from a transport buffer of FIG. 3and FIG. 4. In FIG. 5, the horizontal axis corresponds to an index of aTS packet and the vertical axis indicates the size of data included inthe Bn. FIG. 5 shows the case where as much data as possible is stackedin the main buffer and is then decoded. In this case, the mobile servicedata (or MH data) is also transmitted together with the main servicedata.

As shown in FIG. 5, if audio packet data is transmitted, the audiopacket data is stacked in the Bn 120. If the stacked audio packet datais transmitted to the audio decoder 130 at a time point of DTS(i), onlya small amount of data remains in the Bn 120. If other frames areconsecutively input again, the audio packet data is stacked in the Bn120 again after the time point of DTS(i). However, if the reference timeof a PCR is delayed to prevent underfloor of the TBn 110 as describedabove, then a large amount of data is stacked in the Bn 120 asillustrated in FIG. 6. Namely, since the reference time of the PCR isdelayed, actual decoding time is also delayed and a large amount of datais unexpectedly stacked in the Bn 120, thereby resulting in an overflowphenomenon of the Bn 120.

To remove the overflow phenomenon of the Bn 120, the MH frame controller201, the packet timing/PCR adjustment unit 202, and the auxiliary buffer203 are newly defined as illustrated in FIG. 2 according to theexemplary embodiment of the present invention.

If the digital broadcast transmission system 200 processes broadcastingsignals including the main service data and the mobile service data, thepacket timing/PCR adjustment unit 202 delays the reference time of thePCR based on the size of the mobile service data.

More specifically, the packet timing/PCR adjustment unit 202 delays thereference time of the PCR by a time of 24 to 25 ms, as a result ofcomparing the case where the broadcasting signals including the mainservice data are processed with the case where broadcasting signalsincluding both the main service data and the mobile service data areprocessed. Therefore, when a TS packet satisfying a T-STD model 100 ofFIG. 1 is transmitted through a process for enabling the packettiming/PCR adjustment unit 202 to delay the reference time of the PCR,the underfloor phenomenon of the transport buffer 110 can be prevented.The T-STD model 100 of FIG. 1 may correspond to an MPEG2 T-STD.

The packet timing/PCR adjustment unit 202 or an additional moduleverifies the T-STD model 100 of FIG. 1, based on the PCR of the delayedreference time, before the broadcasting signals are transmitted.Further, the packet timing/PCR adjustment unit 202 determines whetheroverflow of the main buffer 120 of the T-STD model 100 is estimated, asa result of verifying the T-STD model 100.

The packet timing/PCR adjustment unit 202 or the additional modelprevents the T-STD model 100 from overflowing in the main buffer 120,using the determination result. Such an operation is a process forpreventing an overflow phenomenon which may appear in the Bn 120 shownin FIG. 1 as the reference time of the PCR is delayed.

The control process of the packet timing/PCR adjustment unit 202 or theadditional module will now be described in detail.

If the overflow is estimated as the determination result, the packettiming/PCR adjustment unit 202 or the additional module stores a packetreceived in the main buffer 120 in the auxiliary buffer 203. The packettiming/PCR adjustment unit 202 or the additional module replaces thereceived packet with a null packet and performs a control function totransmit a broadcasting signal including the null packet.

The packet timing/PCR adjustment unit 202 or the additional moduleperforms a control operation to store a replacing order in the abovereplacing process, and corrects an order of a packet to be transmittedto an original order using the stored replacing order, duringtransmission of the broadcasting signal.

If the overflow is not estimated as the determination result, the packettiming/PCR adjustment unit 202 or the additional module identifieswhether the packet received in the main buffer 120 is a null packet. Ifthe received packet is the null packet, the packet timing/PCR adjustmentunit 202 or the additional module replaces the null packet with thepacket which has been previously stored in the auxiliary buffer 203 andreturns to the verification process.

FIG. 7 is a flow chart illustrating a data processing method of adigital broadcast transmission system according to an exemplaryembodiment of the present invention.

The digital broadcast transmission system determines whether a packetcorresponds to a PCR packet including PCR information in step S700. Ifthe packet corresponds to a PCR packet in step S700, the digitalbroadcast transmission system delays the reference signal of a PCR instep S701. The delay time may be determined in proportion to the size ofmobile service data and may be a time delay in the range of 24 to 25 ms.More specifically, the time delay may be 24.14 ms.

The digital broadcast transmission system verifies the T-STD model basedon the PCR of the delayed reference time in step S702, beforetransmitting a broadcasting signal. The digital broadcast transmissionsystem determines whether a main buffer of the T-STD model is in a fullstate in step S703, as a result of verifying the T-STD model in stepS702. The full state may mean that the main buffer is completely full oris almost full.

The digital broadcast transmission system prevents the T-STD model fromoverflowing the main buffer using the determination result. Such acontrol process may be implemented using the whole steps or partialsteps of steps S704 to S711 shown in FIG. 7.

If the main buffer is full in step S703, the digital broadcasttransmission system stores the packet received in the main buffer in theauxiliary buffer of the main buffer in step S704 and replaces thereceived packet with a null packet in step S705.

The digital broadcast transmission system determines whether a newpacket corresponds to a PCR packet including PCR information in stepS706. If the new packet does not correspond to a PCR packet, the digitalbroadcast transmission system transmits a broadcasting signal includingthe replaced null packet in step S708. However, if the new packetcorresponds to the PCR packet in step S706, the digital broadcasttransmission system restamps the PCR according to the changed order ofthe packet in step S707.

Another exemplary embodiment for implementing steps S707 and S708 mayinclude a step of storing the packet replacing order in steps S704 andS705, and a step of correcting an order of a packet to be transmitted toan original order using the stored packet replacing order.

Meanwhile, if the main buffer of the T-STD model is not in a full statein step S703, the digital broadcast transmission system identifieswhether the packet received in the main buffer is a null packet in stepS709. If the received packet is a null packet, the digital broadcasttransmission system determines whether another packet has been stored inthe auxiliary buffer in step S710.

If another packet has been stored in step S710, the digital broadcasttransmission system replaces the null packet with the packet stored inthe auxiliary buffer in step S711 and returns to step S702.

FIG. 8 is a block diagram illustrating a digital broadcast receiveraccording to an exemplary embodiment of the present invention. Thedigital broadcast receiver of FIG. 8 can improve reception performanceby performing carrier synchronization recovery, frame synchronizationrecovery, channel equalization, etc. using known data information, thatis inserted into a mobile service data interval in a transmission systemand then is transmitted.

A digital broadcast receiver 800 of the present invention includes atuner 801, a demodulator 802, an equalizer 803, a known sequencedetector 804, a block decoder 805, an RS frame decoder 807, aderandomizer 808, a data deinterleaver 809, an RS decoder 810, and adata derandomizer 811. For convenience of description, the RS framedecoder 807 and the derandomizer 808 will be referred to as a mobileservice data processor, and the data deinterleaver 809, the RS decoder810, and the data derandomizer 811 will be referred to as a main servicedata processor.

The tuner 801 tunes to a frequency of a specific channel anddown-converts the tuned frequency to an intermediate frequency (IF)signal. Then, the tuner 801 outputs the down-converted IF signal to thedemodulator 802 and to the known sequence detector 804.

The demodulator 802 performs automatic gain control, carrier recovery,and timing recovery processes upon the input IF signal, therebyconverting the IF signal into a baseband signal. Thereafter, thedemodulator 802 outputs the baseband signal to the equalizer 803 and tothe known sequence detector 804.

The equalizer 803 compensates for the distortion of a channel includedin the demodulated signal and then outputs the distortion-compensatedsignal to the block decoder 805.

The known sequence detector 804 detects a known data place inserted bythe transmitting system from the input/output data of the demodulator802, that is, the data before or after the demodulation process.Thereafter, the know sequence detector 804 outputs, along with the placeinformation, a symbol sequence of the known data, which is generatedfrom the detected place, to the demodulator 802 and to the equalizer803. The known sequence detector 804 further outputs to the blockdecoder 805 information that is used to allow the block decoder 805 toidentify mobile service data upon which additional encoding is performedin the transmission system and main service data upon which additionalencoding is not performed. Although a connection status is not shown inFIG. 8, the information detected from the known sequence detector 804may be used throughout the entire receiver and may also be used in theRS frame decoder 807.

The demodulator 802 uses the known data symbol sequence during thetiming recovery or carrier recovery, thereby enhancing demodulationperformance. Similarly, the equalizer 803 uses the known data so as toenhance the equalizing performance. Moreover, the decoding result of theblock decoder 805 may be fed back to the equalizer 803, therebyenhancing the equalizing performance.

Meanwhile, if the data input to the block decoder 805 after beingchannel equalized from the equalizer 803 corresponds to data (e.g., datawithin an RS frame) upon which both block encoding and trellis encodingprocesses have been performed by the transmitting system, trellisdecoding and block decoding processes are performed on the input data asinverse processes of the transmission system. Alternatively, if the datainput to the block decoder 805 corresponds to data (e.g., main servicedata) upon which only the trellis encoding has been performed withoutblock encoding, only the trellis decoding process is performed on theinput data.

The data trellis-decoded and block-decoded by the block decoder 805 isinput to the RS frame decoder 807. Namely, the block decoder 805eliminates known data, data used for trellis initialization, signalinginformation data, and an MPEG header, which are inserted in a datagroup, and RS parity data, which is added by thesystematic/non-systematic RS encoder or the non-systematic RS encoder ofthe transmission system. Thereafter, the block decoder 805 outputs theprocessed data to the RS frame decoder 807. The removal of the data maybe performed before the block decoding process, or may be performedduring or after the block decoding process.

Meanwhile, the data trellis-decoded by the block decoder 805 is outputto the main service data processor. The data that is trellis-decoded bythe block decoder 805 and output to the main data processor may includedata and signaling information within the RS frame as well as the mainservice data. Moreover, the RS parity data that is added after thepre-processor of the transmission system may be included in the datathat is output to the main service data processor.

As another exemplary embodiment, the data upon which only the trellisencoding has been performed and the block encoding has not beenperformed by the transmission system may bypass the block decoder 805 soas to be directly input to the main service data processor. In thiscase, a trellis decoder should be provided before the main service dataprocessor. The main service data processor may be designed to be locatedat a position where a signal can be received from the block decoder 805of FIG. 8.

If the input data corresponds to data upon which only the trellisencoding has been performed and the block encoding has not beenperformed in the transmission system, the block decoder 805 may performViterbi decoding on the input data so as to output a hard decision valueor to perform a hard-decision on a soft decision value, and may outputthe result.

Meanwhile, if the input data corresponds to data upon which both theblock encoding and the trellis encoding have been performed in thetransmission system, the block decoder 805 outputs a soft decision valuewith respect to the input data.

More specifically, if the input data corresponds to data upon which theblock encoding has been performed by the block processor of thetransmission system and the trellis encoding has been performed by thetrellis encoder of the transmission system, the block decoder 805performs trellis decoding and the block decoding which are inverseprocesses of the transmission system. In this case, the block processorof the transmission system may be an external encoder and the trellisencoder may be an internal encoder.

To maximize the performance of an external code when decodingconcatenated codes, the decoder of an internal code should output a softdecision value.

Therefore, the block decoder 805 may output a hard decision value on themobile service data. However, when required, it may be more desirablefor the block decoder 805 to output a soft decision value.

Meanwhile, the data deinterleaver 809, the RS decoder 810, and thederandomizer 811 are blocks required for receiving the main servicedata. Therefore, the above-mentioned blocks may not be required in thestructure of a receiving system for receiving only the mobile servicedata.

The data deinterleaver 809 performs an inverse process of the datainterleaver of the transmission system. In other words, the datadeinterleaver 809 deinterleaves the main service data output from theblock decoder 805 and outputs the deinterleaved main service data to theRS decoder 810.

The RS decoder 810 performs a systematic RS decoding process upon thedeinterleaved data and outputs the processed data to the derandomizer811.

The derandomizer 811 receives the output of the RS decoder 810 andgenerates a pseudo random data byte identical to that of the randomizerof the transmission system. Thereafter, the derandomizer 811 performs abitwise exclusive OR (XOR) operation upon the generated pseudo randomdata byte, thereby inserting an MPEG synchronization byte into thebeginning of each packet so as to output data in 188-byte main servicedata packet units.

The RS frame decoder 807 receives only the RS encoded and/or CRC encodedmobile service data from the block decoder 805.

The RS frame decoder 807 performs an inverse process of the RS frameencoder of the transmission system so as to correct errors within the RSframe. Then, the RS frame decoder 807 adds the 1-byte MPEGsynchronization service data packet, which has been removed during theRS frame encoding process, into the error-corrected mobile service datapacket. Thereafter, the RS frame decoder 807 outputs the processed datato the derandomizer 808.

The derandomizer 808 performs a derandomizing process corresponding tothe inverse process of the randomizing process of the transmissionsystem upon the received mobile service data. Therefore, the mobileservice data transmitted from the transmission system can be obtained.

According to the exemplary embodiment of the present invention, thedigital broadcast receiver can process the broadcasting signal includingpackets which do not generate underfloor or overflow.

The tuner 801 receives a broadcasting signal including a main servicedata packet, a mobile service data packet, and a PCR of which referencetime is delayed. A module in charge of the function of the tuner 801 maybe referred to as a receiver.

According to the exemplary embodiment of the present invention, thetuner 801 receives a broadcasting signal including a null data packetinstead of the main service data packet from the digital broadcasttransmission system, according to the verification process result of theT-STD model.

The block decoder 805 demultiplexes the received broadcasting signal. Amodule in charge of the function of the block decoder 805 may bereferred to as a demultiplexer.

The data interleaver 809, the RS decoder 810, and the data derandomizer811 decode the demultiplexed main service data packet using thedemultiplexing result, that is, according to the PCR. A module in chargeof such a function may be referred to as a decoder.

Therefore, according to the exemplary embodiment of the presentinvention, adding the mobile service data to the existing main servicedata can solve all estimated underflow and overflow problems. Forexample, first, the underflow phenomenon in the buffer of the T-STDmodel can be substantially removed by delaying the reference time of thePCR to a prescribed range. Second, the overflow phenomenon in the mainbuffer of the T-STD model can be substantially removed by adding theauxiliary buffer and through a verification process for the T-STD model.

According to the exemplary embodiment of the present invention, theoverflow and underflow problems of the T-STD model can be prevented byadding the MH data to the TS stream satisfying the T-STD.

According to the exemplary embodiment of the present invention, sincethe digital broadcast transmission system pre-checks the underflow andoverflow, the underflow and overflow problems do not occur in the bufferof the digital broadcast receiver.

Meanwhile, in this specification, an article invention and a methodinvention have been described, and the article invention and the methodinvention include similar technical spirits. A description of thearticle invention may be applied to the method invention, andconversely, the method invention may be applied to the articleinvention.

The invention of the method according to the present invention may beimplemented in the form of program commands that are capable of beingperformed through various computer means and then may be recorded incomputer readable media. The computer readable media may include programcommands, data files, data structures, etc. in an independent orcombined form. Program commands recorded in the media may be designedand constructed particularly for the present invention or may be knownto those skilled in the art. The computer readable media includeshardware devices that are configured to store and perform programcommands. For example, the computer readable media includes magneticmedia (e.g., hard discs, floppy discs, and magnetic tapes), opticalmedia (e.g., CD-ROMs and DVDs), magneto-optical media (e.g., flopticaldisks), a ROM, a RAM, a flash memory, etc. The program commands includeadvanced language codes, that can be implemented by a computer using aninterpreter, etc., as well as machine languages, that are configured bya compiler. The aforementioned hardware devices may be constructed to beoperated as one or more software modules for carrying out the operationof the present invention, and an inverse process may be applied.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions.

Thus, it is intended that the present invention covers the modificationsand variations of this invention provided they come within the scope ofthe appended claims and their equivalents.

1-15. (canceled)
 16. A method for transmitting a broadcast signal, themethod comprising: adjusting packet timing and a program clock reference(PCR) of main service data packets; pre-processing mobile service data,wherein the pre-processing comprises: RS (Reed-Solomon)-CRC (CyclicRedundancy check) encoding the mobile service data by adding RS parityand CRC data; block processing the encoded mobile service data by aspecific code rate; forming data groups having the block processedmobile service data, wherein at least one of the data groups includes aplurality of regions; and formatting mobile service data packets havingdata in the data groups; multiplexing the main service data packets andthe mobile service data packets to output multiplexed data packets;post-processing data in the multiplexed data packets, wherein thepost-processing comprises: systematic RS encoding on main service datain the multiplexed data packets; non-systematic RS encoding on mobileservice data in the multiplexed data packets; and interleaving thesystematic and non-systematic RS encoded data; and transmitting atransmission frame including the interleaved data.
 17. The method ofclaim 16, wherein the at least one of the data groups includes knowndata sequences inserted into a specific region of the plurality ofregions.
 18. The method of claim 16, wherein the post-processing furthercomprises randomizing main service data in the multiplexed data packets.19. An apparatus for transmitting a broadcast signal, the apparatuscomprising: an adjustment unit configured to adjust packet timing and aprogram clock reference (PCR) of main service data packets; apre-processor configured to pre-process mobile service data, wherein thepre-processor comprises: an RS (Reed-Solomon)-CRC (Cyclic Redundancycheck) encoder configured to encode the mobile service data by adding RSparity and CRC data; a block processor configured to block process theencoded mobile service data by a specific code rate; a group formatterconfigured to form data groups having the block processed mobile servicedata, wherein at least one of the data groups includes a plurality ofregions; and a packet formatter configured to format mobile service datapackets having data in the data groups; a multiplexer configured tomultiplex the main service data packets and the mobile service datapackets to output multiplexed data packets; a post-processor configuredto post-process data in the multiplexed data packets, wherein thepost-processor comprises: a systematic/non-systematic RS encoderconfigured to systematic RS encode main service data in the multiplexeddata packets and non-systematic RS encode mobile service data in themultiplexed data packets; and an interleaver configured to interleavethe systematic and non-systematic RS encoded data; and a transmissionunit configured to transmit a transmission frame including theinterleaved data.
 20. The apparatus of claim 19, wherein the at leastone of the data groups includes known data sequences inserted into aspecific region of the plurality of regions.
 21. The apparatus of claim19, wherein the post-processor further comprises a randomizer configuredto randomize main service data in the multiplexed data packets.